Heat is your friend when get bolts to let go. Heat to dull red and cool with water. Bolt will fall out. Acetylene torch is more useful than a plasma cutter. It was the original plasma cutter, and will cut through inches of steel than would choke a plasma cuter.
I would agree with Dave, try to salvage your part. I completely redid my suspension last winter. Although my parts were not as rusty as yours, the passenger side (where no power steering fluid could leak and protect the metal from rusting) suspension parts had a fair amount of rust on them. I bought a blasting booth setup and powder coating setup from Eastwood and went to town on my suspension and reused everything but the parts that wear out. After sandblasting and powder coating, my steering arm in particular looked better than it probably looked in 1964. And with the powder coating, the parts will likely never rust again - as long as I'm alive that is. <img src="http://www.impalas.net/forums/images/smilies/smile.gif" border="0" alt="" title="Smile" class="inlineimg" />
Yep thanks guys that’s what I ended up doing took a lot of heat and lotta hammering grinding and etc but eventually came out! Thanks